Cruse control has mind of its own

Looking for some new directions to take on the following problem,

Truck: 2003 KW T600 ( no emissions ) with 400ST2 cummins ISX
Problem: cruse is speeding up or/and re-engauging on its own. With cruse on and no input from driver, the cruse will self engage. I'm assuming that it is going to tha last speed setting but I have never let it get there. Hitting the clutch, brake or throwing the on/off switch will kill it but it has come right back on or comes on later at radom intervals. ( with cruse in ON position, it will not engage if OFF ) Cruse has also been speeding up on its own. At first it was only a couple of mph at a time and that was randomly but this week it is doing almost as soon as the cruse is set and it's going to speed up until I either turn off the cruse or try resetting it via the set/resume switch using the coast feature. Before This week that would normally take care of it ( at least for a while ) but now that does not effect it or if it does, as soon as I let go of the switch it speeds up again. At first I noticed it tended to do the above after a rain storm or truck wash. Now it doesn't matter what the weather is. I have also noticed that if cruse is in the ON position but not engaged, I am getting strange issues with the foot throttle. It first though third gears it with vary from acting normal to studdering or simply losing power. Doesn't matter what you do with throttle, it still will act like it is not receiving input until I either touch the clutch or brake pedal. It then acts normal for the rest of that gear. Next gear will start process all over again. I will have normal operation if the cruse switch is OFF. This just started this week as well. I have already replaced both cruse switches think the problem was there. No difference in operation. Still has problem(s). High idle was working ok most of the time but has been known to speed up and slow down on its own. Now it goes to full and stays there until disengaged. It has been known to speed up idle if switch has been left on when you first start the truck. Turning off switch kills that problem. Ideas??


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Yea, I'm leaning towards ECM as well but wanted some other ideas to check first. Hate to spend that kind of money only to find out it is a broke wire or relay that was the problem.

 

Thanks for your input. A friend has said somewhat the same thing you have just today. I'm taking it into the shop in the morning to have those items looked at as well. This truck is one of those " fly by wire " trucks with no mechanical connection to the motor. I have wondered if it could have been the problem but what is throwing me off is the fact that the truck seems to operate normally with the cruse switch OFF. I too am hoping its simply a wire that's shorting out or a bad speed sensor, ect due to the progression of the problem. That would be so much cheaper than dealing with replacing or rebuilding the ECM.

 

That's always a possibility too but I'm going to hope for more of a mechanical issue

 

Thanks for the input all. I will update the post once I figure out the problem in that it may help another OO in the future.